1. We Can't Get The Main Star(s) Back...We'll Carry On Anyway Right?
Evidence:
Terminator Salvation A mistake every Terminator film made after
Terminator 2: Judgement Day. That, and undoing the closure that the first sequel brought to the saga. It started with the loss of Linda Hamilton's Sarah Connor in
Terminator 3: Rise Of The Machines. But at least we had Arnold Schwarzenegger back as the Terminator himself. (We could have done without those ridiculous star sunglasses though). But to loose him too and continue the franchise without the 'then Governor of California'...well you'd better get the film right. But it didn't. Part of that was down to yet another version John Connor and a recast Kate Brewster. Seriously at this point, the films started to feel like alternate realities of each other. It's something a lot of films suffer with and the Terminator franchise particularly...the merry go round of actors and actresses, meaning there is little continuity between films. Sometimes if you don't have the stars back for the sequel...should you be making it? Other fourth films that fit this 'model':
Species: The Awakening,
Bourne Legacy (Though I rather enjoyed this one!)